The present invention relates generally to electronic circuits and, more particularly to conversion of voltages used in such circuits.
There is often a need to generate a lower DC output voltage from a higher DC input voltage in devices that contain integrated circuits (IC). Voltage converters that perform this function attempt to maintain a stable output voltage and to respond quickly to load transients. Uncontrolled variations in converter output voltage are generally undesirable.
One known circuit for converting voltages is shown in FIG. 1. Voltage converter 100 generates output voltage VOUT from input voltage VIN. As shown, voltage converter 100 includes, in part, a comparator 104 with input hysteresis, a reference voltage generator VREF, a driver 108, an LC filter 116, a voltage divider 112, and a capacitor CFF. Hysteretic comparator 104 generates a control signal Ctrl by comparing reference voltage VREF to a feedback voltage VFB. If feedback voltage VFB exceeds a hysteresis window defined by reference voltage VREF, hysteretic comparator 104 assigns a first value to control signal Ctrl. If, on the other hand, feedback voltage VFB falls below the hysteresis window, hysteretic comparator 104 assigns a second value to control signal Ctrl.
Control signal Ctrl is operative to cause driver 108 to change voltage VX. For example, driver 108 may cause voltage VX to alternate between input voltage VIN and ground. Changes in voltage VX are delivered by inductor L to the converter output VOUT. Voltage divider 112 receives voltage VX and completes a loop by generating feedback voltage VFB and delivering it to an input terminal of hysteretic comparator 104. LC filter 116 is included to attenuate high-frequency noise components that may be present in converter output VOUT, and feedback capacitor CFF is included to modify loop response characteristics.
Persons of ordinary skill in the art will recognize that a voltage drop ΔV is generated between VX and VOUT due to the resistance of inductor L. The relationship between converter output voltage VOUT and inductor voltage drop ΔV can be expressed as VOUT= VX−ΔV, where VX is the average of VX, and is related to VREF as (1+R1/R2)·VREF. Also, as will be clear to those of skill in the relevant art, inductor voltage drop ΔV is related to inductor current IL and its resistance RL as (ΔV=IL·RL). Thus, as shown, voltage drop ΔV directly affects output voltage VOUT and is not controlled or otherwise regulated by voltage converter 100. It is therefore an object of the present invention to reduce the effect of this voltage drop on the converter output voltage and to correspondingly improve the ability of the voltage converter to control its output under changing load conditions.